(Color online) [(a)–(d)] Cross-sectional schematics illustrating the process flow for device fabrication. (a) Oxide etch for diameter circular devices after photolithography on deposited . (b) Molecular self-assembly on . (c) Indirect path, low energy evaporation of thin Au contact using an Ar backfill technique. (d) Direct e-beam evaporated thicker Au layer patterned and etched using conventional lithography and etching.
(Color online) Transmission FTIR spectra (absorbance vs wave numbers) of 1-octadecanethiol (ODT), 1-decanethiol (DMT), and 1,10-decanedithiol (DDT) self-assembled monolayers on GaAs. The units of absorbance are arbitrary. Vertical offsets have been introduced for clarity.
(Color online) characteristics on (a) linear and (b) log scales for diameter circular devices on the control sample and samples with ODT/NDT/XYL/DDT/DMT/BDT monolayers at the interface. Measurements were taken at room temperature in a four probe configuration to eliminate contact resistance effects. The voltage on the axis was applied on the substrate.
(Color online) (a) Low forward-bias Arrhenius plots for the (control) and the six Au/molecule/ samples. (b) Fowler-Nordheim [ vs ] plot for the Au/XYL/ device.
(Color online) (a) Equilibrium energy band diagram for Au/BDT/ structure assuming vacuum at zero energy. The energy scale ( axis) has been modified to include the large BDT band gap. (b) Equilibrium electrostatic potential plots for Au/molecule/ and structures assuming metal Fermi energy, . The molecular layers lower the GaAs surface potential . The GaAs surface is at in all four plots.
(Color online) Current at vs molecular length for symmetric BDT, XYL, NDT, and DDT molecules. (Inset) current at vs dipole moment for ODT, DMT, and DDT molecules.
(Color online) (a) Zero-bias conductance as calculated from the thermionic-field emission model for (Schottky) contacts and from measured electrical data of molecular and control devices , plotted against corresponding GaAs surface potential values obtained from electrostatic analysis of MMS structures. (b) Conductance ratio (molecular:Schottky) for various molecules as calculated from (a).
GaAs surface potential values obtained from electrostatic potential simulations of devices using a Poisson solver. Molecular thickness and molecular dipole moment values used in the simulations are also shown. The metal Fermi level is assumed to be at .
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